1. Field of the Invention
The present invention relates to an electronic apparatus having a plurality of wireless communications blocks, and more particularly, to an electronic apparatus equipped with an oscillator as a clock source shared by each of the wireless communications blocks, for providing a reference clock signal to the wireless communications blocks.
2. Description of the Related Art
Generally, in a wireless communications module, a radio frequency (RF) module receives signals from a remote base station (BS) via the air interface, and the received signals will be demodulated. However, when a frequency offset between the RF module and a corresponding BS is too large, accuracy of the data demodulation may be corrupted. For ensuring demodulation quality of the wireless communications module, it is essential to eliminate the frequency offset (i.e. carrier frequency offset) between the RF module and the corresponding BS. Please refer to FIG. 1. FIG. 1 is a diagram illustrating frequency adjustment of a wireless communications module. In the receiving process, a mixer disposed in the RF module multiplies a high frequency clock signal (e.g. a Local Oscillator (LO) signal) with the received RF signals. The high frequency clock signal may be generated and outputted from an RF frequency synthesizer with reference to a reference clock signal. The frequency of the high frequency clock signal coupled to the mixer should be identical to a frequency of a BS carrier for accurate demodulation, and a wireless communications block operates to remove the carrier frequency offset between the RF module and the BS when the carrier frequency offset is obtained. In FIG. 1, a wireless communications block controls a baseband (BB) module to adjust a frequency of a clock signal (which is outputted from a reference oscillator) by using an Automatic Frequency Control (AFC) unit when a frequency offset is obtained by the BB module at t1. Supposing that a frequency offset between the RF module and the corresponding BS is estimated as β by the baseband module (FIG. 1), the frequency offset may be removed by using the AFC unit to control the oscillator to change its output frequency (i.e. the frequency of the output clock signal) by a frequency variation β. By adjusting the frequency of the clock signal outputted from the oscillator by the frequency variation β, the frequency of the high frequency clock signal (also called “the RF carrier”) becomes the same as the frequency of the BS carrier. Taking a Global System for Mobile Communications/General Packet Radio Service/Enhanced General Packet Radio Service (GSM/GPRS/EGPRS) block as an example, once the frequency offset between the RF module and the BS is removed, the output frequency of the adjusted oscillator is exactly at 26 Mhz.
With the development of electronic technologies, a modern electronic apparatus, such as a mobile electronic device, may be equipped with more than one wireless communications service, such as GSM/GPRS/EGPRS (GGE), Bluetooth, Wireless Fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX) wireless communications service, and so on. A modern mobile electronic device may contain many wireless communications blocks to provide communications services corresponding to different wireless communications standards, respectively. In addition, for reducing the product cost, all the wireless communications blocks of the mobile electronic device may share a single reference oscillator, since the cost of a precise oscillator (e.g. a crystal oscillator) is very high. When one wireless communications block (e.g. a GGE module) removes its carrier frequency offset between the RF module and the corresponding BS without consideration for other wireless communications blocks in the electronic apparatus, performance of the other wireless communications blocks within the electronic apparatus may be degraded due to the dramatic frequency jump of the reference clock signal outputted by the shared oscillator.